1. Field of the Invention
The present invention relates to a composite electronic component comprising a sintered body which is provided therein with an inductor part and a capacitor part, and more particularly, it relates to a composite electronic component for surface mounting.
2. Description of the Background Art
A conventional composite electronic component 1 forming a T filter circuit is described with reference to FIGS. 12 to 14.
Referring to FIG. 12, the composite electronic component 1 is formed by a sintered body having a hexahedral shape. This sintered body is provided with inductor parts 2a and 2b and a capacitor part 3 which is arranged between the inductor parts 2a and 2b. On the other hand, a connection electrode 4 is formed on an upper surface of the sintered body. This connection electrode 4 electrically connects first ends of respective inductor electrodes of the two inductor parts 2a and 2b with a capacitor electrode which is connected to one portion of the capacitor part 3. Further, a ground electrode 5 is formed on a lower surface of the sintered body. This ground electrode 5 is electrically connected to a capacitor electrode which is connected to another portion of the capacitor part 3. First and second signal line electrodes 6a and 6b are formed on both end surfaces of the sintered body. The first and second signal line electrodes 6a and 6b are electrically connected to second ends of the inductor electrodes of the inductor parts 2a and 2b respectively.
FIG. 13 is an exploded perspective view showing the aforementioned composite electronic component 1 in a state before the sintered body is formed. In the composite electronic component 1, the inductor parts 2a and 2b which are formed by inductor green sheets 7a to 7f and 7g to 71 respectively and the capacitor part 3 which is formed by capacitor green sheets 8a to 8f are integrally connected with each other.
The inductor green sheets 7a to 7f are obtained through the following steps: A composition raw material containing a magnetic material of ferrite or the like is blended and mixed with an additive, and calcined. The calcined body obtained is wet-blended by a ball mill or the like, and crushed. The crushed material as obtained is further mixed with a binder or the like, to prepare a slurry. The slurry obtained is molded by a doctor blade coater or a sheet pull method to obtain a green sheet, which in turn is cut into prescribed dimensions.
As clearly understood from FIG. 13, inductor electrodes 10 and connection electrodes 11a and 11b for connecting the inductor electrodes 10 with the exterior are formed on the inductor green sheets 7b, 7j, 7d and 7h respectively. Through holes (not shown) are formed in first ends of the inductor electrodes 10, while second ends of the inductor electrodes 10 are connected to the connection electrodes 11a and 11b respectively. The connection electrodes 11a and 11b are formed to reach edges of the green sheets 7b, 7j, 7d and 7h respectively. Further, additional inductor electrodes 10 are formed on the inductor green sheets 7c and 7i respectively, and through holes (not shown) are formed in first ends of the inductor electrodes 10. The plurality of inductor electrodes 10 are electrically connected with each other via these through holes, to form the inductor part 2a with the inductor green sheets 7a to 7f. Similarly, the plurality of inductor electrodes 10 which are connected with each other via the through holes form the inductor part 2b with the inductor green sheets 7g to 71.
The capacitor green sheets 8a to 8f are obtained through the following steps: A desired composition raw material containing dielectric ceramics having a high dielectric constant is blended and mixed with an additive, and thereafter calcined. The calcined body obtained is wet-blended by a ball mill or the like, and crushed. The crushed material obtained is mixed with a binder or the like, to prepare a slurry. The slurry obtained is sheet-formed by a doctor blade coater or a sheet pull method, and the sheet obtained is cut into desired dimensions to obtain the capacitor green sheets 8a to 8f.
Capacitor electrodes 12a to 12c are formed on the capacitor green sheets 8b to 8d respectively. The capacitor electrodes 12a to 12c are opposed to each other through the capacitor green sheets 8c and 8d respectively, and alternately extend out onto both end surfaces of the capacitor green sheets 8b to 8d. Thus, a laminate of the capacitor green sheets 8a to 8f integrally forms the capacitor part 3.
Intermediate layers 9 are provided between the inductor green sheets 7f and 7g and the capacitor green sheets 8a and 8f respectively. The intermediate layers 9, which are adapted to improve the adhesion between the inductor parts 2a and 2b and the capacitor part 3 after firing, are formed by green sheets obtained by mixing the inductor part material and the capacitor part material with each other and molding the same.
The green sheets 7a to 71, 8a to 8f and 9 shown in FIG. 13 are stacked with each other in the illustrated order, to obtain a laminate. Arrow X shows the stacking direction. This laminate is compression-bonded along the stacking direction X, and fired to obtain a sintered body. A plurality of electrodes are formed on outer surfaces of the sintered body as hereafter described, to obtain the composite electronic component 1.
Referring again to FIG. 12, the connection electrode 4 is formed on the upper surface of the sintered body, for electrically connecting the connection electrodes 11b of the inductor parts 2a and 2b with the capacitor electrodes 12a and 12c respectively. The ground electrode 5 is formed on the lower surface of the sintered body, to extend in parallel with the stacking direction X. This ground electrode 5 is electrically connected to the capacitor electrode 12b. The signal line electrodes 6a and 6b are formed on the end surfaces of the sintered body which are in parallel with the ground electrode 5, i.e., the end surfaces extending along outer surfaces of the inductor parts 2a and 2b and the capacitor part 3. These signal line electrodes 6a and 6b are electrically connected to the connection electrodes 11a of the inductor parts 2a and 2b respectively. Therefore, the ground electrode 5 which is parallel to the stacking direction X is so formed as to reach not only the lower surface of the capacitor part 3 but those of the inductor parts 2a and 2b.
FIG. 14 shows the circuit structure of the composite electronic component 1. As shown in FIG. 14, two inductor parts are connected in series with each other and an end of the capacitor part is connected to the junction between the two inductor parts, to form a T filter.
In the aforementioned composite electronic component 1, however, the ground electrode 5 is formed in parallel with the stacking direction X, so it reaches the lower surfaces of the inductor parts 2a and 2b. On the other hand, the inductor parts 2a and 2b are provided therein with the inductor electrodes 10. Thus, floating capacitances are developed across the ground electrode 5 and the inductor electrodes 10 to deteriorate the high-frequency response, or voltages are applied across the same to deteriorate insulation resistance.